Given and
Find where
I have found
?
So ? cannot be a decimal answer.
Maybe I'm misreading something. How did you calculate this because:
Looking at a binomial probability sums table, I can tell you the answer is not 2. I think you need to recheck your math. If you need help, let me know. Thanks.
Oops! I did misread. I thought p=0.5. My mistake.
Anyway, the answer should be 1, because it's the closest positive integer answer that doesn't cause the binomial probability to go over 0.8.
Using the same symbol (n in this case) to mean two different things in a question is dumb and is no doubt contributing to your confusion. Furthermore, the probability will never equal 0.8 for a discrete value but obviously X can only equal discrete values ....
The question can be repaired (barely) by stating it as follows:
Using trial and error is a reasonable approach to take but, as the previous poster has said, the answer is not x = 2. In fact, the answer to my edited question is x = 1.Originally Posted by Bushy and modified by Mr F